Rotatable indicator having light-emitting diode back-lighting

ABSTRACT

A rotatable indicator, such as a rotatable magnetic position indicating wheel, including a cylindrical drum having opaque and translucent areas defining indicia on the outer drum surface, the drum being rotatably mounted on a supporting member. At least one solid state light-emitting device is provided, such as a lightemitting diode. The light-emitting device is supported on the supporting member within the drum and exposed to the inner surface thereof so that light emitted by the device backilluminates the indicia on the drum.

United States Patent [191 Harden et al.

- 1 May 8, 1973 [54] ROTATABLE INDICATOR HAVING LIGHT-EMITTING DIODEBACK- LIGHTING [75] Inventors: Phillip L. Harden; Samuel M. Thomas, Jr.,both of Fort Wayne, lnd.

[73] Assignee: Bowmar Instrument Corporation,

Fort Wayne, 1nd.

[22] Filed: Dec. 11, 1970 [2]] Appl. No.: 97,168

[52] US. Cl. ..340/373, 240/2.1, 250/217 SS,

340/378 R [51] Int. Cl. ..G01d 11/28, H05b 33/00 [58] Field of Search..240/2.l; 250/217 85;

340/378 A, 378 R; 313/108 D, 109.5; 116/DIG. 35, 124.4

[5 6] References Cited UNITED STATES PATENTS 3,372,260 3/1968 Bell..116/124.4 X

Steinke ..240/2.1 X

3,500,391 3/1970 Heske ..340/378 A 3,581,162 5/1971 Wheatley ..2S0/217SS X 3,264,640 8/1966 Ducharme et al. .....340/378 A 3,278,740 10/ 1 966Madansky ..240l2.l

3,596,136 7/1971 Fischer ..313/l08 D 3,480,950 11/1969 Rachman ..340/378R Primary ExaminerDonald O. Woodiel Assistant Examiner-Daniel M. YasichAtt0rneyl-lood, Gust, Irish, Lundy 81. Coffey [57] ABSTRACT A rotatableindicator, such as a rotatable magnetic position indicating wheel,including a cylindrical drum having opaque and translucent areasdefining indicia on the outer drum surface, the drum being rotatablymounted on a supporting member. At least one solid state light-emittingdevice is provided, such as a lightemitting diode. The light-emittingdevice is supported on the supporting member within the drum and exposedto the inner surface thereof so that light emitted by the deviceback-illuminates the indicia on the drum.

7 Claims, 10 Drawing Figures PAIENTEM- @1573 3,732,560

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PATENTEWY 81m 3.732.560

SHEET 2 [IF 2 INVENTORS; PH|LLIP L. HARDEN, SAMUEL H. THOMAQIJRATTORNEYS ROTATABLE INDICATOR HAVING LIGHT- EMITTING DIODE BACK-LIGHTINGBACKGROUND OF THE INVENTION 1 Field of the Invention This inventionrelates generally to rotatable indicators, and more particularly to arotatable indicator which is back-lighted by a solid statelight-emitting device.

2. Description of the Prior Art Rotary magnetic position indicators arecommonly employed for displayingdiscreet indicia in response to thecharacters of a prearranged code. A common type of such indicatorcomprises a diametrically polarized permanent magnet rotor and a statorstructure having selectively energizable field windings thereon, therotor carrying a drum having the indicia displayed 'on it surface.Selective energization of the field windings causes the magnetic axis ofthe rotor to align itself with the respective poles of the fieldstructure which are energized, thereby to provide the desired rotationalindication.

It is frequently required that the indicator be lighted. Various typesof front-lighting have been provided with the light illuminating thefront surface of the drum and the indicia thereon, however, shadows,stray light and glare have been objectionable features of suchfrontlighting. It has therefore been considered desirable to provideback-lighting of the drum and indicia, light from a source disposedwithin the drum illuminating translucent areas on the drum which definethe indicia. Such back-lighting has heretofore been provided by aconventional incandescent lamp. In certain applications, particularly inairborne installations, such rotary magnetic position indicators arehighly miniaturized, the drum typically having a diameter less than oneinch. Back-lighting of such miniature indicators with incandescent lampshas been difficult, it being necessary to accommodate an extremely tinybulb within an ex-' tremely confined space. Such tiny bulbs are fragile,

requiring frequent replacement, which, in turn, necessitates removal ofthe indicator from the panel and partial disassembly thereof. Further,the glowing filament of an incandescent lamp has necessitated provisionfor diffusion of the light, and appreciable heat is generated by thelamp which requires provision for dissipation.

It is therefore desirable to provide a back-lighted rotary indicatorwhich does not employ an incandescent lamp.

It is well known that certain semiconductors having a p-n junctionformed therein will emit light when an appropriate potential is appliedacross the junction. Further discussion of this phenonenon is containedin an article entitled Light-emitting Semiconductors by Fredrick F.Morehead, Jr., appearing in the Scientific American for May, 1967, pages109-121. Such lightemitting diodes may be energized from a low voltage,direct or alternating current source, are highly reliable, rugged, andmay be extremely small in size. Of the many semiconductor compoundswhich possess electroluminescent properties, in varying degrees, only alimited number, including gallium phosphide and gallium arsenidephosphide, have been found to have the desired efficiency, brightness,reliability and reproducability. Such light-emitting diodes thus lendthemselves to use in back-lighting rotatable indicators, particularlythose which are highly miniaturized.

SUMMARY OF THE INVENTION The invention, in its. broader aspects,provides a rotatable indicator comprising a cylindrical drum havinginner and outer surfaces, the drum having opaque and translucent areasdefining indicia on the outer surface. A supporting member is providedwith means for rotatably mounting the drum thereon. At least one solidstate light-emitting device is provided with means for supporting thedevice on the supporting member within the drum and exposed to the innersurface thereof. Means are provided for electrically connecting thedevice to a source of energizing potential, the light emitted by thedevice thus back-illuminating the indica on the drum. In the preferredembodiment, the solid state light-emitting device comprises alight-emitting diode.

It is accordingly an object of the invention to provide an improvedback-lighted rotatable indicator.

Another object of the invention is to provide an improved back-lightedrotatable indicator utilizing a light emitting diode as the lightsource.

The above-mentioned and other features and objects of this invention andthe manner of attaining them will become more apparent and the inventionitself will be best understood by reference to the following descriptionof an embodiment of the invention taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front cross-sectional viewshowing a rotary magnetic position indicator back-lighted in accordancewith the invention;

FIG. 2 is a side cross-sectional view taken generally along the line 2-2of FIG. 1;

FIG. 3 is a fragmentary view showing the outer surface of the drum ofthe indicator of FIGS. 1 and 2;

FIG. 4 is an enlarged cross-sectional view taken along the line 4-4 ofFIG. 3 and showing one embodiment of the drum;

FIG. 4A is a view similar to FIG. 4 and showing another embodiment ofthe drum;

FIG. 5 is a fragmentary, top cross-sectional view taken generally alongthe line 55 of FIG. 2 and showing the light-emitting diode assembly ingreater detail;

FIG. 6 is a front view of the light-emitting diode assembly taken alongthe line 6-6 of FIG. 5;

FIG. 7 is a fragmentary, side cross-sectional view taken generally alongthe line 7-7 of FIG. 5;

FIG. 8 is an enlarged cross-sectional view taken along the line 8--8 ofFIG. 6; and

FIG. 9 is a schematic diagram showing the electrical connection of thelightemitting diodes employed in the embodiment of the previous figures.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the figures ofthe drawing, there is shown a rotary magnetic position indicator,generally indicated at 10. Indicator 10 comprises a supporting board 12formed of suitable, rigid insulating material. Shaft 14 is secured toboard 12 and extends forwardly therefrom, as shown. Suitableanti-friction bearings 16 are positioned on shaft 14 and rotatablysupport rotor assembly 18.

Rotor assembly 18 comprises indicator drum 20 having an outercylindrical drum portion 22 and an inner annular flange portion 24.Annular permanent magnet 26 is adhered to flange portion 24, flangeportion 24 and magnet 26 being mounted on bearings 16, drum 20 andpermanent magnet 26 thus rotating as a unit on bearings 16. Permanentmagnet 26 is conventionally diametrically oppositely polarized, as shownin FIG. 1.

Stator assembly 28 comprises an annular yoke portion 30 which may beformed of suitable sintered magnetic material. Spacers 32 are equallyspaced around core 30 to define coil-receiving sections 34, twelve beingshown in the illustrated embodiment. Field windings 36 are respectivelywound on sections 34 of core 30 between insulators 32. Stator assembly28 is supported on board 12 by means of metal pins 38 secured toinsulators 32 and extending through suitable openings in board 12. Therespective ends of field windings 36 may be connected to pins 38 andappropriate connections (not shown) to pins 38 may be printed on therear surface of board 12. Field windings 36 may be connected in themanner disclosed in US. Pat. No. 3,478,349 to Buuck et al. and assignedto the assignee of the present invention. It will be readily understoodthat with permanent magnet 26 being diametrically polarized, as shown,energization of selective ones of field windings 36 will cause themagnet axis of magnet 26 to align itself with the resulting magneticpoles formed in stator yoke 30, thereby rotating drum 20, as shown byarrows 39, so that a corresponding discrete indicia appearing on theouter surface of flange 22 is displayed through a viewing window (notshown).

In the embodiment of FIG. 4, drum 20 may be molded from suitablenear-transparent or highly translucent plastic material, a materialhaving a water-white color being preferred. The inner surface 40 offlange 22 is preferably lightly sprayed with white paint, as at 42.Outer surface 44 of flange 22 is lithographed with black paint or ink,as at 46, to define the desired indicia 48, which may be conventionalalpha-numeric characters. It will thus be seen that illumination of theinner surface outer projections 68, 70, and an intermediate projection72 which is formed upwardly away from upper surface 74 of plate 52. Rod56 has its end 74 extending through hole 76 in board 12 and is securedto the rear surface thereof as by solder 78. The portion of rod 56projecting forwardly of board 12 is somewhat flattened and has adownwardly curved portion 78. The forwardly extending portion of rod 56adjacent its outer end and adjacent board 12 is insulatingly secured toprojections 68, 70 of plate 52, as by epoxy adhesive 80, 82.Intermediate curved portion 78 of rod 56 is likewise insulatinglysecured to projection 72, as by epoxy adhesive 84.

In the illustrated embodiment, a pair of elongated, strip,light-emitting diodes 86, 88 are mounted on upper surface 74 of plate52, light-emitting diodes 86, 88 being transversely spaced-apart in thedirection 39 of rotation of drum 20, as indicated in FIG. 1, andextending forwardly from board 12, as best seen in FIG. 5. As best seenin FIG. 8, each of the light-emitting diodes 86, 88 has P and N sectionsjoined by a junction 90, top and bottom surfaces 92, 94 and oppositesides 96, 98. In a specific embodiment, gallium arsenide phosphide(GaAsP) light-emitting diodes are employed with light being emitted fromtop surface 92 in response to excitation of the diode. A relatively thinsheet 100 of insulating material is adhered to bottom surface 94 and, inturn, is adhered to top surface 74 of plate 52.

In the specific embodiment, each of the diodes 86, 88 has fourelectrical leads 102 welded to and extending from side 96 of its Psection, and one electrical lead 104 welded to and extending from side98 of its N section. Leads 102 of diode 86 are electrically connected torod 56 and lead 104 is electrically connected to plate 52. Leads 102 ofdiode 88 are electrically connected to plate 52, and lead 104 isconnected to rod 56.

40 of flange 22 of drum 20 will result in back-lighting of indicia 48.

In the preferred embodiment of FIG. 4A, drum 20 may be molded from clearor naturalcolor plastic material and outer surface 44 of flange 22 islightly sprayed with white or some other color paint, as at 42a. Paintedsurface 42a is then lithographed with black paint or ink, as at 46, todefine indicia 48. Thus, in this embodiment, the indicia may appear incolors other than white.

In order to back-light indicia 48 on flange 22 of drum 20,light-emitting diode assembly 50 is provided disposed between innersurface 40 of flange 22 of drum 20 and stator assembly 28. Referring nowparticularly to FIGS. 5 through 9, light-emitting diode assembly 50comprises a metal platform or support plate 52 which is arcuately curvedto conform to the curvature of inner' surface 40 of flange 22 of drum20. Support plate 52 is supported on mounting board 12 by a pair ofmetal posts 54, 56. Post 54 is directly, conductively secured to plate52 adjacent its end 53, as by welding at 58. End 62 of support rod 54extends through hole 60 in board 12 and is secured to the rear surfacethereof, as by solder 64. The other end 66 of plate 52 has a pair ofReference to FIG. 9 will reveal that with this particular electricalconnection of diodes 86, 88, they diodes are coupled in parallel,oppositely polarized relationship, this connection being particularlysuited for energization from an alternating current source, such as a400 cycle source. A trimming resistor 106 may be coupled in series, asshown in FIG. 9. It will be readily apparent that external electricalconnections for energizing lightemitting diodes 86, 88 may be connectedto ends 62, 74 of rods 54, 56, and may be printed on the rear surface ofboard 12, along with the electrical connections to stator windings 36.

It will be readily understood that the particular arrangement,configuration and electrical connection of the light-emitting diodes isillustrative only, and that other semiconductors, such as galliumphosphide (GaP), other diode configurations, a greater or lesser numberof diodes, and other electrical connections of the diodes may beemployed. Thus, a larger number, such as six, relatively small galliumphosphide diode chips may be employed electrically coupled in paralleland polarized in the same direction rather than being oppositelypolarized as in the illustrated embodiment. It will further beunderstood that one surface of each diode may be directly conductivelysecured to plate 52, as by welding or soldering. It will also beunderstood that an electroluminescent panel may be employed rather thanlight-emitting diodes.

It will be seen that in the illustrated embodiment metal plate 52 servesnot only as a supporting platform for the light-emitting diodes, butalso serves as a heat sink to dissipate heat from the diodes. However,it will be understood that individual diode chips or bars may be mountedin .a molded plastic supporting element or platform also carryingelectrical connections such as insert pins, printed or depositedconductors, or the like. It will also be understood that light-emittingdevices which emit light from any or all surfaces may be supported on ametal or insulating material platform.

It will be seen that back-lighting of the indicator by the use oflight-emitting diodes provides uniform illumination of the indicia onthe drum with no shadows or stray light. The light-emitting diodesoperate on low voltage, occupy considerably less space and generate lessheat than incandescent lamps. The light-emitting diodes are considerablymore reliable, have substantially longer life, and are much more ruggedthan miniature incandescent lamps, there being no filament to burn outor break, the light-emitting diode backlighted indicator of theinvention thus lending itself to miniaturization and being especiallysuited for applications involving severe environmental conditions, suchas vibration and/or wide temperature variations. Further, by employing aplurality .of light-emitting diodes, upon failure of one diode, theremaining diode or diodes will still emit sufficient light to illuminatethe indicia on the drum. The light-emitting diodes provide more uniformlight output over a greater surface area as compared with a miniatureincandescent lamp and thus less light diffusion is required.

While there have been described above the principles of this inventionin connection with specific apparatus, it is to be clearly understoodthat this description is made only by way of example and not as alimitation to the scope of the invention.

What is claimed is:

l. A rotatable indicator comprising a cylindrical drum having inner andouter surfaces, said drum having opaque and translucent areas definingindicia on said outer surface, a rigid supporting board of insulatingmaterial; means for rotatably mounting said drum on said board; at leastone solid state light-emitting device; means for supporting said deviceon said board within said drum in a position exposed to said innersurface thereof, said supporting means including a metal plate and firstand second spaced metal posts secured to said board and extendingoutwardly therefrom within said drum, said plate being conductivelysecured to one of said posts and insulatingly secured to the other ofsaid posts; said device being a light-emitting diode having generallyplanar surfaces with light being emitted from one of said diodesurfaces, said one diode surface facing said inner drum surface, theother of said diode surfaces being supported on said plate whereby lightemitted by said device back-illuminates said indicia, said diode havingP and N sections joined by a junction intermediate and generallyparallel with said diode surfaces, means for electrically connectingsaid device to a source of operating potential, said connecting meansincluding at least one electrical connection connecting one of .saidsections to said plate and at least one other electrical connectionconnecting the other of said sections to said other post.

. The indicator of claim 1 wherein said plate 18 curved generally toconform to said inner drum surface, said one diode surface beingadjacent said inner drum surface.

3. The indicator of claim 2 wherein there are a plurality of saiddiodes.

4. The indicator of claim 3 wherein each of said diodes comprises anelongated strip, said strips being spaced-apart in the direction ofrotation of said drum and extending outwardly from said board.

5. The indicator of claim 4 wherein said other surfaces of said diodesare adhered to a relatively thin sheet of insulating material, saidsheet being adhered to said plate.

6. The indicator of claim 5 wherein each of said strips has oppositesides, said connections comprising at least one electrical leadconnecting one of said section of each strip on one side thereof to saidplate and at least one electrical lead connecting the other of saidsections of each strip on the other side thereof to said other post.

7. The indicator of claim 6 wherein there are two said strips, saidleads connecting the P section of one strip and the N section of theother strip to said plate, and the N section of said one strip and the Psection of said other strip to said other post, whereby said devices arecoupled in parallel and in oppositely polarized relationship across saidsource.

III i

1. A rotatable indicator comprising a cylindrical drum having inner andouter surfaces, said drum having opaque and translucent areas definingindicia on said outer surface, a rigid supporting board of insulatingmaterial; means for rotatably mounting said drum on said board; at leastone solid state light-emitting device; means for supporting said deviceon said board within said drum in a position exposed to said innersurface thereof, said supporting means including a metal plate and firstand second spaced metal posts secured to said board and extendingoutwardly therefrom within said drum, said plate being conductivelysecured to one of said posts and insulatingly secured to the other ofsaid posts; said device being a lightemitting diode having generallyplanar surfaces with light being emitted from one of said diodesurfaces, said one diode surface facing said inner drum surface, theother of said diode surfaces being supported on said plate whereby lightemitted by said device back-illuminates said indicia, said diode havingP and N sections joined by a junction intermediate and generallyparallel with said diode surfaces, means for electrically connectingsaid device to a source of operating potential, said connecting meansincluding at least one electrical connection connecting one of saidsections to said plate and at least one other electrical connectionconnecting the other of said sections to said other post.
 2. Theindicator of claim 1 wherein said plate is curved generally to conformto said inner drum surface, said one diode surface being adjacent saidinner drum surface.
 3. The indicator of claim 2 wherein there are aplurality of said diodes.
 4. The indicator of claim 3 wherein each ofsaid diodes comprises an elongated strip, said strips being spaced-apartin the direction of rotation of said drum and extending outwardly fromsaid board.
 5. The indicator of claim 4 wherein said other surfaces ofsaid diodes are adhered to a relatively thin sheet of insulatingmaterial, said sheet being adhered to said plate.
 6. The indicator ofclaim 5 wherein each of said strips has opposite sides, said connectionscomprising at least one electrical lead connecting one of said sectionof each strip on one side thereof to said plate and at least oneelectrical lead connecting the other of said sections of each strip onthe other side thereof to said other post.
 7. The indicator of claim 6wherein there are two said strips, said leads connecting the P sectionof one strip and the N section of the other strip to said plate, and theN section of said one strip and the P section of said other strip tosaid other post, whereby said devices are coupled in parallel and inoppositely polarized relationship across said source.